Senate Democratic Leader Harry Reid voluntarily interviewed with Justice Department lawyers and FBI agents a year ago as they were investigating Sen. Robert Menendez for possible corruption, according to sources familiar with the matter.

There is no indication authorities believe Reid acted improperly or that he might be ensnared in the case: He hasn’t met with investigators since he spoke with them in the spring of 2014, or appeared before a grand jury looking into the allegations against Menendez, the sources said.

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But the involvement of the then-Senate majority leader, who now runs the Democratic minority, highlights the seriousness of both the investigation and the problem Reid has on his hands in dealing with a member in his ranks who’s expected to be indicted within weeks.

Reid’s interview with DOJ lawyers and FBI agents focused on his interaction with Menendez and Salomon Melgen, a close friend of the New Jersey Democrat and a big donor. The Menendez-Melgen relationship is at the heart of the federal criminal investigation, and Menendez had sought Reid’s help in assisting the Florida ophthalmologist resolve a multimillion-dollar billing dispute his company was having with the federal government.

Neither Reid’s office nor DOJ would comment on the Democratic leader’s meeting with federal authorities. The interview, which lasted roughly an hour, was not recorded, sources said; investigators took notes. The sources characterized Reid as simply a witness in the case.

At the very least, though, the case is a major political challenge for Reid: It would be the first time in his decade as Senate party leader that he would have to handle the fallout of an indicted Democratic senator. He would have to choose between standing behind a fellow Democrat who proclaims his innocence or distancing himself and his Democratic colleagues from the scandal. The fact that Menendez sought Reid’s help on Melgen’s behalf further complicates matters for the minority leader.

Reid will face pressure to remove Menendez from his spot as ranking Democrat on the influential Senate Foreign Relations Committee, even though there are no explicit caucus rules requiring an indicted senator to step down from committee leadership posts.

Speaking to reporters Monday evening, Menendez would not say if he would step down from the position once the indictment is unsealed.

“You know what? I haven’t been charged of anything so you guys are way ahead,” Menendez said. “Hope you’re right at the end, for your reporting purposes.”

Republicans are already attacking Reid over the matter. The National Republican Senatorial Committee is demanding that Reid return $10,000 Menendez donated to him. And GOP leaders are openly suggesting that Menendez should step aside from his committee spot, even though he hasn’t been indicted yet.

“Typically, when these kinds of charges are brought, people step aside from their leadership positions,” Senate Majority Leader Mitch McConnell (R-Ky.) said Sunday on CBS’ “Face the Nation.” “But that will be up to the Democratic leader, Sen. Reid, to make that call.”

Reid’s involvement in the matter began after Menendez intervened with the Centers for Medicare & Medicaid Services on Melgen’s behalf during a June 7, 2012, meeting with Marilyn Tavenner, then acting head of the agency, regarding a multimillion-dollar billing dispute with Melgen’s company, Vitreo-Retinal Consultants. Menendez later had a follow-up call with Tavenner, according to the New Jersey Law Journal, which reported last week on a legal dispute between Menendez and DOJ over whether the senator’s aides must answer questions from a federal grand jury hearing the case.

While he was getting help from Menendez and Reid, Melgen made a huge donation to a pro-Democratic super PAC run by former Reid aides. Melgen’s company donated $400,000 to Senate Majority PAC in June 2012, followed by an additional $300,000 in mid-October 2012, according to Federal Election Commission records. Menendez was up for reelection in 2012, and most of Melgen’s donation to the super PAC was poured into the New Jersey Senate race. Melgen family members also gave $33,700 to Menendez’s 2012 reelection campaign, plus a further $50,000 to the New Jersey Democratic State Committee.

In addition, Melgen flew Reid on his company’s private plane in June 2012 from Washington to Boston and back for a Senate Majority PAC event. The super PAC reported reimbursing Melgen’s company $4,160 for “travel.” Though the group’s filing with the FEC does not specify who went on the trip, Reid’s office later confirmed to POLITICO that the payment was for the senator’s fundraising swing to Boston.

Having Reid, then Senate majority leader, meet with Sebelius over Melgen demonstrates the extraordinary lengths to which Menendez was willing to go to help out his longtime friend and political benefactor, as well as how far Reid would go to aid one of his rank-and-file Democrats.

Senate Democrats have long griped that the Obama administration has not been responsive to their requests, so Reid, at times, has agreed to intervene and lobby senior officials so that issues important to his caucus would land on the administration’s radar. The Sebelius meeting appears to be no different.

The expected indictment of Menendez would become the highest-profile case DOJ’s Public Integrity Section has brought against a sitting U.S. senator since 2008, when GOP Sen. Ted Stevens of Alaska faced felony charges for failing to report gifts. After Stevens was indicted, he was forced to give up his ranking member position on the Senate Appropriations Committee.

Similarly, in 2009, then-Sen. John Ensign (R-Nev.) gave up a leadership post after he revealed an extramarital affair with a campaign aide. And in 2010, New York Rep. Charles Rangel gave up his spot as the top Democrat on the Ways and Means Committee when he came under investigation by the Ethics Committee over his failure to pay taxes from income on a vacation home.

Menendez, who has set up a legal-defense fund to cover the costs of the long-running criminal investigation, has repeatedly denied wrongdoing, and he has vowed to remain in office even if indicted.

“Let me be very clear, very clear. I have always conducted myself appropriately and in accordance with the law,” Menendez said at a Friday news conference. “I am not going anywhere.”

Some conservatives, including Texas Sen. Ted Cruz, have suggested that the White House is behind the looming Menendez indictment, pointing out that the New Jersey Democrat has been very vocal in his opposition to President Barack Obama’s policies on Cuba and Iran.

Yet Menendez has been under federal scrutiny for more than two years, ever since the conservative Daily Caller reported in November 2012 that Menendez had sex with underage prostitutes at Melgen’s home in a resort in the Dominican Republic.

While those allegations could not be substantiated, the media frenzy over the case focused attention on Menendez’s relationship with Melgen, who, in addition to his medical practice, made a fortune selling a data company.

Menendez was forced to personally repay nearly $70,000 for unreported flights on Melgen’s plane. And federal investigators have looked extensively into Menendez’s intervention with the departments of State and Commerce on Melgen’s behalf. That includes his efforts to secure U.S. government help in pressuring the Dominican Republic to honor a $500 million contract with a port security company owned by Melgen.

In July 2012, Menendez raised the issue with State Department officials during a Senate Foreign Relations subcommittee hearing.

A Menendez aide has refused to answer questions to the federal grand jury about this issue as well, according to the New Jersey Law Journal.